They are indeed quite challenging. We literally wrote a paper about it (https://arxiv.org/abs/2605.09114) ... you almost describe some of our original architecture too! You might find it interesting -- or not. https://getswytch.com

> Ya this problem was solved 20 years ago with Varnish cache and Coral cache/CDN.

It was... if you are paying datacenter rates for the bandwidth

If you're paying cloud provider per GB pricing, nah, even text will add up if you happen to be targeted by a bunch of bots

> What went wrong is that nobody solved stuff like Russian doll caching in a general way separate from the programming language and database. We should have had ways to make dependency graphs using Etag headers as keys with real cache invalidation of dependent data.

we did that with nested ESI includes in Varnish so every "box" of content on the page was cached separately + some piping for invalidation, so if a given piece in the database was changed it sent invalidation to all nodes. There was also some grace so if the thing you wanted got updated RIGHT NOW you might get stale version while the new one is updated in background, and don't pay the latency cost